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TEHRAN, Iran (CNN) -- Iran's ambassador to the United Nations has urged U.N. Secretary General Kofi Annan and the U.N. Security Council to stop "Washington's illegal and impudent threats against Iran," the state-run Iranian news agency IRNA reported.

Later in the day, the United Nations acknowledged having received the letter.

"U.S. officials are impudently threatening Iran with use of force in blatant contravention of international law and the basic principles of United Nations Charter," Mohammad Javad Zarif said in the letter.

"U.S. threats against Iran have found new dimension to the extent that U.S. dailies are publishing stories about possibility of aggression on Iran and whether the U.S. would use nuclear arms against Iran and the U.S. officials do not reject such stories," the letter said.

The letter quoted U.S. President George W. Bush as saying in a media conference on April 18, 2006, in response to a question whether the U.S. would initiate a nuclear attack against Iran, that "all options are on the table."

Zarif said that U.S. threats to initiate a nuclear attack against Iran also had jeopardized the Non-Proliferation Treaty.

He called for immediate action by U.N. Security Council to stop U.S. threats against Iran.